U.S. Pat. No. 4,115,878 describes a method for admitting air into the water outlet, i.e., suction line of a spa, to prevent excessive suction when the outlet becomes blocked. The patented system may operate satisfactorily in a hot tub or spa which is relatively deep, e.g., filled with water to a depth of 29-48 inches. However, the present invention is concerned primarily with drain-and-fill tubs which are filled to an average depth of only about 15-17 inches. When an attempt is made to use the patented system in a drain-and-fill tub of the kind with which the present invention is concerned, the system has a tendency to become unstable, for example, water bounces up and down in the vent tube under dynamic conditions of operation. When this happens air is sucked into the pump. This, of course, interferes with the proper operation of the pump because of the air passing through it.
In view of these and other deficiencies of the prior art, it is the primary object of the invention to provide a dynamically balanced system for preventing dangerous and excessive suction at the suction fitting in the spa, tub, or pool by allowing air to enter the pump when the suction fitting is plugged but at the same time preventing air from entering the pump when the suction fitting is not plugged.
It is important to provide an adequate supply of air when the suction fitting does become plugged so, for example, a person will not be injured if one's hand or other part of the body covers the suction outlet of the tub. Another object is to achieve these results without use of moving parts such as mechanically or electrically operated valves and accompanying electrical circuitry such as a vacuum switch. Still, another object is to provide a dynamic balance that will automatically slow down the flow of water whenever a person using the tub obstructs the suction fitting but which at other times pumps water through the outlet at or near maximum efficiency. A further object is to provide an automatic method of dynamic control which is self-regulating so that a greater compensating effect is provided when the output of the pump is increased if a longer pump is used. Yet another more specific object of the invention to provide a relief system as described which operates quickly and gently and in addition begins to function gradually as the object is brought into proximity with the suction fitting so that a person is not hurt by placing a hand over the suction fitting.
It has also been previously proposed to employ a vacuum operated electrical switch to turn off the pump motor when suction becomes excessive. This system is unsatisfactory since it is sensitive to water impurities such as lint or scum and therefore, may fail under dangerous circumstances.
In view of these and other deficiencies in the prior art, the invention will now be described by way of example with reference to the specification and the accompanying figures.